Long time lurker here.
HI, and welcome
No, you aren't crazy, but it does sound like there is something going on. My unprofessional guess would be an anxiety disorder.
I would contact a Neuropsychologist for an evaluation. They can do testing, rule out other things, and get a diagnosis. you can then see a therapist, counselor, or Psychiatrist for meds if needed.
A child may HAVE ADHD, but it is not what they ARE. Never tell a child they ARE ADHD.
Wow...OK, I'll ditto her--possibly anxiety, but in any case, go pursue a diagnosis/professional help.
Sleep: Those *hours* sound like enough to me, though I expect there are kids for whom it isn't enough. IS he sleeping enough? Is he really tired at any point during the day? Dark circles (though those can have other causes)? I ask 'cause one thing my older kid had was sleep apnea--he'd stop breathing every so often, for 15+ seconds, not the scary infant kind, but the older-kid (he was in 1st grade when he had surgery). We actually didn't really quite notice it until we looked closely--we'd always know it happened, but tended to think it was just "normal", it was so much part of his pattern. The tonsil & adenoid removal made a huge difference in the *quality* of his sleep. It's one of the things you can have that mimics ADHD, and I can imagine the lack of sleep would mess with other things. NOT that I think your kid has this or anything, but more to ask about quality rather than quantity!
You say no problems at ALL in school? He may be one of those kids who can basically hold it all together for as long as school is & then falls apart when he gets home from all the stress of holding it together?
Honestly, you've done the whole list of things you can do on your own. Go get professional help. It doesn't mean you end up medicating automatically, and even if you do, there are many worse things to do to your kid! Far better to get help at age 6 than wait for the pre-teens & teens--better he learns coping strategies now!
OMG - you are not crazy - please follow the help other posters have given you.
Sounds like you have alot on your hands, but try not to be so hard on yourselves. I would recommend making an appointment with a specialist, a ped just won't fit the bill for the kind of issues our kids need help with! :).